fix error if no cron job in first deployment

mac@lowang · mac@lowang · commit 8faf3fd3310d · 2018-09-26T12:18:01.000+08:00
diff --git a/playbooks/roles/cronjob/tasks/main.yml b/playbooks/roles/cronjob/tasks/main.yml
@@ -1,5 +1,5 @@
 - name: backup old crontab
-  shell: crontab -l > ~/backup.cron
+  shell: crontab -l > ~/backup.cron  2> /dev/null || true
 
 - name: copy image-clean script
   copy:
